Six tris(aryloxy)phosphorothionates substituted in the para position of the aromatic rings were synthesized and studied by 31P NMR, X-ray diffraction techniques and ab initio calculations at a RHF/6-31G** level of theory, in order to find the main structural factors associated with the δ31P in these compounds. As the electron-withdrawing (EW) ability of the substituents was increased, an ‘abnormal’ shielding effect on δ31P of the arylphosphorothionates was observed. The analyses of the geometrical properties obtained through both experimental and theoretical methods showed that a propeller-type conformation is preferred for the arylphosphorothionates, except in the case of the tris(O-4-methylphenyl)phosphorothionate, since one of the aromatic rings is not rotated in the same direction as the other two in the solid state. The main features associated with the δ31P NMR of compounds 1–6 were a decrease of the averaged O–P–O angle and mainly the shortening of the PS bond length, which is consistent with an increase of the thiophosphoryl bond order as δ31P values go upfield. On the other hand, comparison of the experimental and calculated bond lengths and bond angles involving α bonded atoms to phosphorus of the six compounds suggested that stereoelectronic interactions of the type nπO-σ*PS, nπO-σ*P-OAr and nπS-σ*P-OAr could be present in the arylphosphorothionates 1–6.
The substituent effects on the 31P NMR chemical shifts of a series of six arylphosphorothionates [SP(OAr)3] are analyzed in terms of the changes observed in the geometries of the compounds by experimental and theoretical methods.